Let’s focus on let in JavaScript in detail.

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🔹 let in JavaScript

The let keyword is used to declare block-scoped variables in JavaScript.
👉 Introduced in ES6 (2015) to fix issues with var.

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1️⃣ Syntax

let variableName = value;

Example:

let age = 20;
let name = "Raj";

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2️⃣ Features of let

✅ Block Scope

• A variable declared with let is only available inside the block { } where it is declared.

{
  let x = 10;
  console.log(x); // 10
}
// console.log(x); ❌ Error (x not accessible outside block)

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✅ Cannot Redeclare in Same Scope

• You cannot redeclare the same variable within the same block.

let a = 5;
// let a = 10; ❌ Error: Identifier 'a' has already been declared
a = 10;   // ✅ Reassignment is allowed
console.log(a); // 10

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✅ Reassignment is Allowed

• Unlike const, variables declared with let can be reassigned.

let city = "Delhi";
city = "Mumbai"; // ✅ Allowed
console.log(city); // Mumbai

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✅ Hoisting with Temporal Dead Zone (TDZ)

• let is hoisted but not initialized.
• Using it before declaration causes an error.

// console.log(x); ❌ ReferenceError (TDZ)
let x = 100;
console.log(x); // 100

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✅ Works Better in Loops

• let creates a new variable for each loop iteration, unlike var.

for (let i = 0; i < 3; i++) {
  setTimeout(() => console.log(i), 1000);
}
// Output: 0, 1, 2  ✅ (correct behavior)

If we used var, all outputs would be 3.

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3️⃣ When to Use let?

• When you need a variable that:
  • Is limited to a block { }.
  • May be reassigned later.
• Example: counters, temporary values, loop variables.

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✅ Summary

• Block-scoped (exists only inside { }).
• Cannot redeclare in the same scope.
• Can be reassigned.
• Hoisted but in the Temporal Dead Zone until initialized.
• Safer than var, preferred in modern JS.